The present invention relates to a temperature and humidity control apparatus in an air-conditioning system used for drying photosensitive materials and also used for general purposes.
Conventionally, the following temperature and humidity control methods are used for controlling the temperature and relative humidity in a workshop to be accurately constant.
(1) One method is described as follows. Temperature control is conducted independently from humidity control, wherein temperature control is conducted by a cooling dehumidifier and a heater, and humidity control is conducted by a cooling dehumidifier and a humidifier. When cooling is temporarily conducted by the temperature control and dehumidification is conducted by humidity control, a larger opening is adopted for the cooling dehumidifier.
(2) Another method is described as follows. After temperature and humidity have been temporarily controlled lower than the set values using a cooling dehumidifier, temperature is controlled by a heater, and humidity is controlled by a humidifier.
(3) Still another method is described as follows. The opening of a cooling dehumidifier is added to the opening of a heater and also added to the opening of a humidifier, and an amount of forward control corresponding to the entrance temperature and humidity is added to each opening (disclosed in Japanese Patent Publication Open to Public Inspection No. 181112/1989).
Temperature and humidity of the discharge side air of a heat exchanger, which are used when the control system of the heat exchanger is designed, are expressed as follows.
(4) A heat exchanger is divided into a finite number of portions, and the temperature of the discharge side air is expressed in accordance with the heat balance in each portion, which is disclosed in the thesis written by Hideaki Kano, the title of which is "Discrete System Approximate Model of the Distribution Constant System" in the magazine of "Measurement and Control" vol. 19-11, 1044/1050 published in 1980.
(5) Still another method is described as follows. A heat exchanger used as a cooling dehumidifier is divided into a finite number of portions. In accordance with the heat balance and the material balance in each portion, the temperature and humidity of the discharge side air are simultaneously expressed when the humidity close to a heating surface is given to a model, which is disclosed in the thesis "S. Chandra Sheker and G. Green, Dynamic Study of a Chill Water Cooling and Dehumidifying Coil, ASHRAE TRANSACTIONS, 76-3141, 36/51 (6,1970)".
Five methods are described above, however, however, each method has a disadvantage, which will be described as follows.
In the case of method (1), when the temperature and humidity setting is in a condition of cooling and dehumidifying, either the control of temperature or the control of humidity is neglected, so that the control deviation is increased.
In the case of method (2), after air has been unnecessarily cooled and humidified, it is heated and humidified again. Therefore, energy is wasted, and this method is not economical.
FIG. 6 is a graph showing a state of control of temperature and humidity in the case of method (3). FIG. 7 is a graph showing the changes of an amount of high temperature fluid in the heater, an amount of low temperature fluid in the cooling dehumidifier, and an amount of steam in the humidifier.
In the case of method (3), the following problems may be encountered. According to FIGS. 6 and 7, in order to cancel an amount of cooling conducted by the cooling dehumidifier, the opening of the cooling dehumidifier is added to the opening of the heater, however, the effect provided by a simple addition is not so high due to a difference between the cooling dehumidifier and the heater and also due to a difference between the low and high temperature fluids. Therefore, an adjustment of trial and error is conducted in this method. Concerning the addition of an amount of feed forward control corresponding to the entrance temperature and humidity, the circumstances are the same as those described above. Even after the adjustment conducted in the manner of trial and error, there is a possibility that the temperatures of the low and high temperature fluids fluctuate. In this case, it is impossible to provide a sufficiently high accuracy.
In the case of method (4), only a change in temperature at an outlet of the heat exchanger is expressed, and simultaneous changes in the temperature and humidity are not expressed.
In the case of method (5), simultaneous changes in the temperature and humidity in the cooling dehumidifier are expressed by the Lewis Number, which is a constant, and humidity Wf, which is a humidity at a position close to the surface of heat transfer tube, wherein Wf changes in accordance with a wet condition on the surface of heat transfer tube. The Lewis Number is a constant at all times, however, the value of Wf changes in accordance with a wet condition of the surface of the heat transfer tube portion between air and low temperature fluid when the humidity of the entrance portion is changed. Further, it is necessary to change the value of Wf in accordance with a flow amount region to be used for each row. Therefore, it is difficult to use this method when the entrance humidity is frequently changed or the flow amount is changed. Further, it is necessary to respectively find a film coefficient of heat transfer on the air side, a coefficient of heat-transfer of the heat transfer tube portion between air and low temperature fluid, and a film coefficient of heat transfer on the low temperature fluid side. In order to find the above coefficients, it is necessary to arrange temperature sensors to measure the temperature distribution in the cooling dehumidifier.
Due to the foregoing, it can be said that the temperature and humidity are difficult to be predicted under the various temperature and humidity conditions, using the prediction apparatus of (4) and (5).